The present invention may be efficiently implemented in a single VLSI integrated circuit of low cost. The present invention provides for a very high channel count, limited only be the speed and-cost of the circuit and the average degree of upward pitch shifting required. Also, the present invention allows for use of multiple interpolator circuits to be used with a single waveform memory.
The present invention relates to electronic musical instruments, and more particularly to digital sampling instruments which create musical notes by reproducing recorded waveforms of musical instruments or sound effects, or mathematically calculated waveforms from a waveform memory at a variable playback rate. As has been previously disclosed in the above-identified cross-referenced patent application Ser. No. 07/462,392 filed Jan. 5, 1990 one technique for improving the performance of such instruments is the use of a cache memory and waveform interpolation. Such a technique increases the available channel count of the instrument by eliminating the waveform memory access time bottleneck which limits performance. While the basic use of cache memory has been previously described, there are several improvements beyond the preferred embodiment described in patent application Ser. No. 07/462,392 which are described herein.
It is an object of the present invention to provide improved N point interpolation variable pitch playback of musical sounds. The techniques so described can be efficiently implemented in the preferred embodiment by a single VLSI circuit of low cost. The preferred embodiment allows a very high channel count which will support many simultaneous musical notes. It also allows memory systems having variable access times, as well as the use of more than one interpolator circuit or chip with a single sound waveform memory.
Further described are techniques to optimize the performance of the system by decreasing the complexity of the VLSI circuit required to implement cache memory. Another technique described improves the cache system by increasing the degree to which upward pitch shifting on a minority of the channels can occur.
Other objects, features and advantages of the present invention will become apparent from the following detailed description when taken in conjunction with the accompanying drawings.